A method for establishing a prediction model of low-cycle fatigue life of exhaust heat end

Abstract

The application discloses a kind of prediction model establishment methods of exhaust heat end low cycle fatigue life, comprising the following steps: according to engine at different power, set different exhaust heat end model thermal boundary condition;According to each boundary condition respectively to exhaust heat end model is carried out stress field analysis, obtains the strain table of the maximum equivalent plastic strain increment of exhaust heat end and the temperature table of the maximum equivalent plastic strain increment corresponding node;According to the maximum equivalent plastic strain increment of exhaust heat end determines exhaust heat end life check component;Based on the temperature value in temperature table respectively to check component carries out high temperature tensile test and cold thermal shock cycle test, obtains the static tensile table of the material of life check component under corresponding temperature and test life table;According to static tensile table, test life table and strain table determine the prediction model of exhaust heat end, to predict the fatigue life of exhaust heat end, it is convenient to set up reasonably for the overhaul and replacement cycle of exhaust heat end.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of engines, and particularly relates to a method for establishing a life prediction model of low-cycle fatigue of an exhaust heat end. BACKGROUND

[0002] The exhaust heat end is an important component of an engine, and bears high-temperature load and vibration load during the working process of the engine. The exhaust heat end is a component prone to reliability failure in the engine. For a supercharged engine, the risk of reliability failure of the exhaust heat end is increasingly prominent due to the increase in thermal load of the entire exhaust heat end, the increase in temperature amplitude and mechanical load amplitude. Therefore, the life of the exhaust heat end directly affects the reliability of the engine. However, the low-cycle life of the exhaust heat end has not been predicted in the prior art. SUMMARY

[0003] Therefore, the main purpose of the present application is to provide a method for establishing a life prediction model of low-cycle fatigue of an exhaust heat end, which is used for predicting the low-cycle life of the exhaust heat end.

[0004] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0005] The present application provides a method for establishing a life prediction model of low-cycle fatigue of an exhaust heat end, comprising:

[0006] establishing an exhaust heat end model;

[0007] setting thermal boundary conditions of the exhaust heat end model according to different powers of the engine;

[0008] respectively performing stress field analysis on the exhaust heat end model based on each of the thermal boundary conditions to obtain a strain increment table of a maximum equivalent plastic strain increment of the exhaust heat end and a temperature table of a node position corresponding to the maximum equivalent plastic strain increment;

[0009] determining a life checking component according to the maximum equivalent plastic strain increment of the exhaust heat end;

[0010] respectively performing high-temperature tensile tests on the life checking component of the exhaust heat end based on the temperature table to obtain a static tensile fracture strain table of a material of the life checking component at a corresponding temperature;

[0011] respectively performing cold-hot impact cycle tests on the life checking component based on the temperature table to obtain a test life table of the life checking component at the corresponding temperature;

[0012] determining the prediction model according to the static tensile fracture strain table, the test life table and the strain increment table, wherein the prediction model is used for predicting the low-cycle fatigue life of the exhaust heat end.

[0013] Further, the step of determining the prediction model according to the static tensile fracture strain table, the test life table and the strain increment table specifically comprises:

[0014] According to the static tensile fracture strain table of the life inspection component, the fatigue ductility coefficient table of the life inspection component is determined;

[0015] According to the fatigue ductility coefficient table, the test life table and the strain increment table, the fatigue ductility index table of the life inspection component is determined;

[0016] According to the fatigue ductility coefficient table and the fatigue ductility index table, the prediction model is obtained, and the expression of the prediction model is:

[0017]

[0018] Wherein, N f is the predicted life, C is the fatigue ductility coefficient, β is the fatigue ductility index, Δε p is the maximum equivalent plastic strain increment.

[0019] Further, the thermal boundary condition of the exhaust heat end model comprises:

[0020] Forced convection heat transfer between high-temperature gas and the inner surface of the exhaust heat end, free convection heat transfer between engine cabin air and the outer surface of the exhaust heat end, thermal radiation between the exhaust heat end and the heat shield, and thermal conduction of the intake flange and the cylinder head.

[0021] Further, the step of obtaining the thermal boundary condition of the exhaust heat end further comprises the boundary condition at the turbine outlet, wherein the boundary condition at the turbine outlet is obtained according to the turbine inlet mass flow, the rotating speed of the turbine blade and the rotating angle of the turbine blade.

[0022] Further, the step of obtaining the strain table of the maximum equivalent plastic strain increment of the exhaust heat end specifically comprises:

[0023] Setting the cold-heat shock analysis step of the exhaust heat end model;

[0024] Based on the cold-heat shock analysis step, sequentially coupled thermal stress analysis is performed on the exhaust heat end model to obtain the maximum equivalent plastic strain increment of the exhaust heat end;

[0025] Based on different maximum equivalent plastic strain increments, a strain increment table of the maximum equivalent plastic strain increment is obtained.

[0026] Further, the cold-heat shock analysis step is greater than or equal to three cold-heat shock cycles.

[0027] Further, based on the cold-heat shock analysis step, sequentially coupling thermal stress analysis is performed on the exhaust heat end model to obtain the maximum equivalent plastic strain increment of the exhaust heat end, specifically comprising:

[0028] Each maximum equivalent plastic strain increment in the strain increment table is based on the sequentially coupled thermal stress analysis to obtain the first equivalent plastic strain of each node of the exhaust heat end model at the last step of the last cycle of the cold-heat shock cycle;

[0029] Based on the sequentially coupled thermal stress analysis, the second equivalent plastic strain of the each node of the exhaust heat end model at the last step of the second last cycle of the cold-heat shock cycle is obtained;

[0030] The first equivalent plastic strain of the each node is subtracted from the corresponding second equivalent plastic strain of the each node to obtain the equivalent plastic strain increment of the each node, and the maximum equivalent plastic strain increment is obtained according to the equivalent plastic strain increment of the each node.

[0031] Further, the method for establishing the prediction model of the low-cycle fatigue life of the exhaust heat end according to any one of the above, further comprises the following steps:

[0032] According to the prediction model, a life prediction program is obtained.

[0033] Further, the life prediction program obtained according to the determined prediction model further comprises:

[0034] The life prediction program is embedded in the ABAQUS software, and the calling and execution of the life prediction program is realized in the form of interface operation buttons of the ABAQUS software.

[0035] Further, according to the determined prediction model, the maximum equivalent plastic strain increment of the exhaust heat end is substituted into the life prediction program to obtain the predicted life of the exhaust heat end.

[0036] The application provides a prediction model establishment method of exhaust heat end low cycle fatigue life, which comprises the following steps: establishing an exhaust heat end model; setting a thermal boundary condition of the exhaust heat end according to different powers of an engine; performing stress field analysis on the exhaust heat end model based on each thermal boundary condition to obtain a strain table of maximum equivalent plastic strain increment of the exhaust heat end and a temperature table of the node position corresponding to the maximum equivalent plastic strain increment; determining a life checking component according to the maximum equivalent plastic strain increment of the exhaust heat end; performing high-temperature tensile test on the life checking component of the exhaust heat end based on the temperature table to obtain a static tensile fracture strain table of the material of the life checking component at the corresponding temperature; performing cold-heat impact cycle test on the life checking component based on the temperature table to obtain a test life table of the life checking component at the corresponding temperature; and determining the prediction model according to the static tensile fracture strain table, the test life table and the strain increment table. The thermal boundary condition of the exhaust heat end is set according to different power states of the engine, stress field analysis is performed on the exhaust heat end, the strain increment table of the maximum equivalent plastic strain increment of the exhaust heat end and the corresponding temperature table are obtained, high-temperature tensile test and cold-heat impact cycle test are respectively performed on the life checking component according to the temperature table, the static tensile fracture strain table and the test life table of the life checking component are obtained, and the prediction model is determined according to the static tensile fracture strain table, the test life table and the strain increment table, so as to predict the low cycle fatigue life of the exhaust heat end. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 A flowchart of a prediction model establishment method of exhaust heat end low cycle fatigue life is provided for the embodiments of the application.

[0038] Figure 2 A flowchart of step S7 in another prediction model establishment method of exhaust heat end low cycle fatigue life is provided for the embodiments of the application.

[0039] Figure 3 An analysis diagram of a boundary condition at a turbine outlet is provided for the embodiments of the application.

[0040] Figure 4 A flowchart of step S3 in another prediction model establishment method of exhaust heat end low cycle fatigue life is provided for the embodiments of the application.

[0041] Figure 5 A flowchart of step S32 in another prediction model establishment method of exhaust heat end low cycle fatigue life is provided for the embodiments of the application. DETAILED DESCRIPTION

[0042] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not intended to limit the present application.

[0043] In the specific embodiments, various specific technical features described can be combined in any suitable manner without contradiction, for example, different embodiments and technical solutions can be formed by combining different specific technical features. In order to avoid unnecessary repetition, various possible combinations of various specific technical features in the present application are not described again.

[0044] In the following description, the terms "first", "second", and the like are only used to distinguish different objects, and do not mean that the objects have the same or related relationship. It should be understood that the positional description "upper", "lower", "outer", "inner" is the position in the normal use state, and the "left" and "right" directions represent the left and right directions shown in the specific corresponding schematic diagram, which can be the left and right directions in the normal use state or not.

[0045] It should be noted that the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus including a series of elements includes not only those elements, but also other elements not explicitly listed, or other elements inherent to such a process, method, article or apparatus. Without more limitations, the element defined by the statement "including a" does not exclude the presence of additional identical elements in the process, method, article or apparatus including the element. The term "connected" includes direct connection unless otherwise specified.

[0046] The exhaust heat end is an important component of the engine, and due to the harsh working environment, it bears high temperature and vibration load during operation, and is also a component prone to reliability failure in the engine. For a supercharged engine, the entire exhaust heat end becomes heavier, the entire heat end becomes longer, and there are more components, so it is more prone to durability failure problems. The failure of the exhaust heat end will cause the engine to malfunction, so predicting the low-cycle life of the exhaust heat end is beneficial to reasonably setting the maintenance and replacement period of the exhaust heat end.

[0047] Therefore, the embodiments of the present application provide a method for establishing a prediction model of the low-cycle fatigue life of the exhaust heat end, which is used in combination with simulation data and a prediction model to predict the low-cycle fatigue life of the exhaust heat end, shorten the development cycle, and save the development cost.

[0048] The exhaust heat end to which the prediction model establishment method provided in the following specific embodiments is applied can be an exhaust heat end of any vehicle type. Exemplarily, the exhaust heat end can be applied to a passenger car, and the exhaust heat end can also be applicable to a truck.

[0049] In an embodiment, as shown in Figure 1 Figure 1 A prediction model establishment method for low-cycle fatigue life of an exhaust heat end is provided. The flow of the prediction model establishment method comprises the following steps:

[0050] S1, establishing an exhaust heat end model;

[0051] S2, setting thermal boundary conditions of the exhaust heat end model according to different powers of an engine;

[0052] S3, respectively performing stress field analysis on the exhaust heat end model based on each thermal boundary condition to obtain a strain increment table of a maximum equivalent plastic strain increment of the exhaust heat end and a temperature table of a node position corresponding to the maximum equivalent plastic strain increment;

[0053] S4, determining a life checking component according to the maximum equivalent plastic strain increment of the exhaust heat end;

[0054] S5, respectively performing high-temperature tensile tests on the life checking component based on the temperature table to obtain a static tensile fracture strain table of a material of the life checking component at a corresponding temperature;

[0055] S6, respectively performing cold-hot impact cycle tests on the life checking component based on the temperature table to obtain a test life table of the life checking component at the corresponding temperature;

[0056] S7, determining a prediction model according to the static tensile fracture strain table, the test life table and the strain increment table, wherein the prediction model is used to predict the low-cycle fatigue life of the exhaust heat end.

[0057] Specifically, the exhaust heat end model is established, wherein the exhaust heat end model comprises a simplified cylinder head, a bolt, an exhaust manifold body, a supercharger shell, a supercharger flange, a front-stage exhaust pipe intake pipe, a catalyst shell, an exhaust tail pipe, an exhaust flange, an oxygen sensor base, a heat shield, a fixing bracket, a weld, etc. For example, the cylinder head, the bolt, the exhaust manifold body, the supercharger shell, the supercharger flange and the exhaust flange are meshed by tetrahedral elements, and the remaining components of the exhaust heat end are meshed by shell elements. It should be understood by those skilled in the art that the exhaust heat end model can be constructed by using finite element software.

[0058] ​The thermal boundary conditions of the exhaust heat end model are set according to different powers of the engine. Specifically, the steady-state internal flow field of the exhaust heat end under different engine powers is calculated by using STRA-CCM+ respectively, the internal gas temperature of the exhaust heat end is obtained, the convective heat transfer coefficient of the exhaust heat end model is set, and the internal gas temperature and the convective heat transfer coefficient of the exhaust heat end model are mapped to the finite element grid on the inner surface of the exhaust heat end as the thermal boundary conditions of the exhaust heat end model, that is, the thermal boundary conditions of the exhaust heat end model corresponding to different engine powers are obtained. It should be noted that the convective heat transfer coefficient of the exhaust heat end model includes: the free convection heat transfer coefficient of the engine compartment air and the outer surface of the exhaust heat end, the thermal radiation coefficient between the exhaust heat end and the heat shield, the thermal conductivity coefficient of the intake flange and the cylinder head, the thermal conductivity coefficient of the cylinder head bolt and the intake flange, the thermal conductivity coefficient of the supercharger flange and the front exhaust pipe flange, and the thermal conductivity coefficient between the exhaust heat end parts, the internal gas temperature of the exhaust heat end model and the convective heat transfer coefficient of the exhaust heat end model can be obtained by CFD software analysis.

[0059] According to different thermal boundary conditions, stress field analysis is performed on the exhaust heat end model to obtain a strain increment table of the maximum equivalent plastic strain increment of the exhaust heat end and a temperature table at the node of the maximum equivalent plastic strain increment of the exhaust heat end. Specifically, one maximum equivalent plastic strain increment and the temperature at the corresponding node can be obtained under one thermal boundary condition, stress field analysis is performed on the exhaust heat end model under each thermal boundary condition to obtain the corresponding maximum equivalent plastic strain increment of the exhaust heat end and the temperature value at the maximum equivalent plastic strain increment, and the obtained maximum equivalent plastic strain increment data and the temperature data of the corresponding node are made into a strain increment table and a temperature table respectively. It should be noted that the stress field parameters generally include stress, strain and displacement, the strain increment can be obtained according to the strain value, and the strain increment table and the temperature table are corresponding relationship, that is, one temperature value in the temperature table corresponds to one maximum equivalent plastic strain increment value in the strain increment table.

[0060] According to the maximum equivalent plastic strain increment of the exhaust heat end, the life checking component is determined. Specifically, the position of the maximum equivalent plastic strain increment in the exhaust heat end is determined as the life checking component by performing stress field analysis on the exhaust heat end. For example, in the stress field analysis result, the maximum equivalent plastic strain increment of the exhaust heat end occurs on the exhaust manifold body of the exhaust heat end, that is, the material damage of the exhaust manifold body in the exhaust heat end is the most serious, and the exhaust heat end is selected as the life checking component to reflect the life of the exhaust heat end. It should be noted that the life prediction result of the life checking component is the life prediction result of the exhaust heat end.

[0061] The high-temperature tensile test is performed on the life inspection component based on the temperature table to obtain a static tensile fracture strain table of the material of the life inspection component at the corresponding temperature. Specifically, a plurality of test bars made of the same material as the inspection component are prepared, the number of the test bars is consistent with the number of temperature data in the temperature table, each temperature in the temperature table is taken as a temperature condition of the high-temperature tensile test, the high-temperature tensile test is performed on the test bars, the static tensile fracture strain at the corresponding temperature is obtained, and all the static tensile fracture strain data obtained by the experiment are made into a static tensile fracture strain table. It should be noted that the static tensile fracture strain table and the temperature table are in a corresponding relationship, that is, one temperature value in the temperature table corresponds to one strain value in the static tensile fracture strain table.

[0062] The cold-heat impact cycle test is performed on the life inspection component based on the temperature table to obtain a test life table of the life inspection component at the corresponding temperature. Specifically, a plurality of test pieces are prepared, the material and structure of the test pieces are the same as those of the life inspection component, the number of the test pieces is consistent with the number of temperature data in the temperature table, each temperature in the temperature table is taken as a temperature condition of the cold-heat impact cycle test, the cold-heat impact cycle test is performed on the test pieces, the test life at the corresponding temperature is obtained, and all the test life data obtained by the experiment are made into a test life table. It should be noted that the test life table and the temperature table are in a corresponding relationship, that is, one temperature value in the temperature table corresponds to one life value in the test life table.

[0063] After the static tensile fracture strain table, the test life table and the strain increment table are obtained, a prediction model is determined according to the static tensile fracture strain table, the test life table and the strain increment table, the low-cycle fatigue life of the exhaust hot end is predicted through the prediction model, so as to predict the fatigue life of the exhaust hot end, and facilitate reasonable setting of the maintenance and replacement period of the exhaust hot end, thereby saving the maintenance cost.

[0064] In an embodiment, as Figure 2 S7, the step of determining the prediction model according to the static tensile fracture strain table and the test life table, specifically includes:

[0065] S71, determining a fatigue ductility coefficient table of the life inspection component according to the static tensile fracture strain table of the life inspection component;

[0066] S72, determining a fatigue ductility index table of the life inspection component according to the fatigue ductility coefficient table, the test life table and the strain increment table;

[0067] S73, obtaining the prediction model according to the fatigue ductility coefficient and the fatigue ductility index of the life inspection component.

[0068] Specifically, the fatigue ductility coefficient table corresponding to the life inspection component is calculated according to the static tensile fracture strain table of the life inspection component, and the relationship expression between the static tensile fracture strain and the fatigue ductility coefficient is C = 0.5 x ε f , wherein C is the fatigue ductility coefficient, ε f is the static tensile fracture strain, each static tensile fracture strain value in the static tensile fracture strain table is substituted into the relationship expression between the static tensile fracture strain and the fatigue ductility coefficient to obtain the corresponding fatigue ductility coefficient data, and the fatigue ductility coefficient table is made according to the obtained fatigue ductility coefficient data. It should be noted that the static tensile fracture strain table is obtained based on the temperature table and the high temperature tensile test, each data in the static tensile fracture strain table corresponds to each data in the temperature table, that is, one temperature value in the temperature table corresponds to one static tensile fracture strain value in the static tensile fracture strain table, and since each data in the fatigue ductility coefficient table is calculated according to each data in the static tensile fracture strain table, each data in the fatigue ductility coefficient table corresponds to each data in the fatigue ductility coefficient table, that is, one temperature value in the temperature table corresponds to one static tensile fracture strain value in the static tensile fracture strain table and one fatigue ductility coefficient value in the fatigue ductility coefficient table.

[0069] Specifically, the fatigue ductility index table of the life inspection component is determined according to the fatigue ductility coefficient table, the test life table and the strain increment table. The fatigue ductility index is calculated according to the fatigue ductility coefficient and the test life, and the calculation relationship satisfies the Manson-Coffin equation: Δε p N β = C, wherein Δε p is the maximum equivalent plastic strain increment, N is the test life, β is the fatigue ductility index, and C is the fatigue ductility coefficient. It should be noted that Δε pThe strain increment table is used to obtain N, the test life table is used to obtain C, and the fatigue ductility coefficient table is used to obtain C. The temperature table corresponds to the strain increment table, the test life table, and the fatigue ductility coefficient table, respectively. That is, a temperature value in the temperature table corresponds to a maximum equivalent plastic strain increment in the strain increment table, a test life value in the test life table, and a fatigue ductility coefficient in the fatigue ductility coefficient table. Therefore, a MAP diagram can be constructed using the Manson-Coffin equation from the strain increment table, the test life table, the fatigue ductility coefficient table, and the fatigue ductility index table. Using the strain increment table, the test life table, and the fatigue ductility coefficient table as input values, the fatigue ductility index table can be obtained. It should be noted that since the fatigue ductility coefficient table, the fatigue ductility index table, and the temperature table are corresponding, a MAP diagram of the fatigue ductility coefficient table, the fatigue ductility index table, and the temperature table can also be constructed. That is, at a certain temperature, a fatigue ductility coefficient value corresponds to a fatigue ductility index value.

[0070] The prediction model is obtained based on the fatigue ductility coefficient table and the fatigue ductility index table. The expression of the prediction model is as follows: Where, N f To predict lifespan, C is the fatigue ductility coefficient, β is the fatigue ductility exponent, and Δε is... p The maximum equivalent plastic strain increment is given by Δε. C is obtained from the fatigue ductility coefficient table, and β is obtained from the fatigue ductility index table. It should be noted that since the fatigue ductility coefficient table, fatigue ductility index table, and temperature table are correlated, the maximum equivalent plastic strain increment Δε at the exhaust hot end is calculated using finite element software. p and equivalent plastic strain increment Δε p The temperature value at the node is used to find the corresponding fatigue ductility coefficient C and fatigue ductility exponent β based on the temperature value at the node with the maximum equivalent plastic strain increment. Δε p Substituting C and β into the prediction model expression, we obtain the predicted lifetime N. f Based on the obtained predicted lifetime N f This is beneficial for rationally designing the maintenance and repair cycle of the exhaust hot end. The node location with the maximum equivalent plastic strain increment is located at the check component of the exhaust hot end, and the fatigue ductility coefficient C and fatigue ductility index β in the prediction model expression are the material parameters of the check component.

[0071] In one embodiment, the thermal boundary conditions of the exhaust hot end model include: forced convection heat transfer between the high-temperature gas and the inner surface of the exhaust hot end, free convection heat transfer between the engine compartment air and the outer surface of the exhaust hot end, thermal radiation between the exhaust hot end and the heat shield, thermal conduction between the intake flange and the cylinder head, and thermal conduction between the fixed bracket and the engine block.

[0072] Specifically, the internal gas temperature of the exhaust heat end model and the convective heat transfer coefficient of the exhaust heat end model can be analyzed by CFD software, and then the internal gas temperature and the convective heat transfer coefficient are mapped to the finite element grid of the inner surface of the exhaust heat end, the thermal radiation coefficient between the exhaust heat end and the heat shield, the thermal conductivity coefficient between the intake flange and the cylinder head, and the thermal conductivity coefficient between the fixed support and the engine cylinder are all selected as corresponding empirical coefficients according to the set exhaust heat end material and the actual working condition, to serve as the thermal boundary conditions of the exhaust heat end model.

[0073] In an embodiment, the thermal boundary conditions of the exhaust heat end further include boundary conditions at the turbine outlet, wherein the boundary conditions at the turbine outlet are obtained according to the turbine inlet mass flow, the rotational speed of the turbine blade, and the rotation angle of the turbine blade.

[0074] Specifically, as shown in Figure 3 , the gas velocity direction at the turbine outlet is divided into tangential velocity u* and circumferential velocity u, and the resultant velocity of the gas is v h , the resultant velocity v h is decomposed into axial velocity v ax and circumferential velocity , wherein u = ω x r, ω is the rotational speed of the turbine blade, and r is the radius of the turbine blade; the velocity m is the turbine inlet mass flow, ρ is the gas density, and s is the turbine outlet area; the circumferential velocity β is the included angle between the tangential velocity u* and the axial velocity v ax . According to the analysis of the gas velocity at the turbine outlet, the circumferential velocity and the axial velocity at the turbine outlet are defined by parameters such as the turbine inlet mass flow, the rotational speed of the turbine blade, and the rotation angle of the turbine blade, to obtain the boundary conditions at the turbine outlet. The code is written and embedded into the finite element software, to serve as the thermal boundary conditions of the exhaust heat end.

[0075] In an embodiment, as shown in Figure 4 , the step of obtaining the strain increment table of the maximum equivalent plastic strain increment of the exhaust heat end includes:

[0076] S31, setting a cold-heat shock analysis step of the exhaust heat end model;

[0077] S32, performing sequential coupled thermal stress analysis on the exhaust heat end model based on the cold-heat shock analysis step, to obtain the maximum equivalent plastic strain increment of the exhaust heat end;

[0078] S33, tabulating based on different maximum equivalent plastic strain increments, to obtain the strain increment table of the maximum equivalent plastic strain increment.

[0079] Specifically, a cold-heat shock analysis step of the exhaust heat end model is set, and a sequential coupling thermal stress analysis is performed on the exhaust heat end model to obtain the maximum equivalent plastic strain increment of the exhaust heat end. The cold-heat shock analysis step is set under different thermal boundary conditions to perform the sequential coupling thermal stress analysis, and different maximum equivalent plastic strain increments are obtained. The different maximum equivalent plastic strain increments are made into a strain increment table.

[0080] In an embodiment, the cold-heat shock analysis step is greater than or equal to three cold-heat shock cycles. Specifically, one cold-heat shock cycle is from room temperature to high temperature. The temperature change of the exhaust heat end model under cold-heat shock is at least referred to three cold-heat shock cycles. Since the temperature change of the exhaust heat end model tends to be stable in three cold-heat shock cycles, in order to reduce the calculation amount of the finite element software and improve the calculation efficiency, the cold-heat shock analysis step is set to three cold-heat shock cycles, so that the temperature change calculation of the cold-heat shock considers both accuracy and efficiency.

[0081] In an embodiment, as shown in FIG. 3, based on the cold-heat shock analysis step, the sequential coupling thermal stress analysis is performed on the exhaust heat end model to obtain the maximum equivalent plastic strain increment of the exhaust heat end, and the step specifically includes: Figure 5

[0082] S321, each maximum equivalent plastic strain increment in the strain increment table is obtained based on the first equivalent plastic strain of each node of the exhaust heat end model at the last step of the last cycle of the cold-heat shock cycle in the sequential coupling thermal stress analysis;

[0083] S322, the second equivalent plastic strain of each node of the exhaust heat end model at the last step of the second last cycle of the cold-heat shock cycle is obtained based on the sequential coupling thermal stress analysis;

[0084] S323, the equivalent plastic strain increment of each node is obtained by subtracting the second equivalent plastic strain of each node from the first equivalent plastic strain of each node, and the maximum equivalent plastic strain increment is obtained according to the equivalent plastic strain increment of each node.

[0085] ​Specifically, the sequential coupling thermal stress analysis is performed on the exhaust heat end model, the first equivalent plastic strain of each node at the last step of the last cycle of the cold-heat shock cycle is exported in the post-processing module of the finite element software, the second equivalent plastic strain of each node at the last step of the second last cycle of the cold-heat shock cycle is further exported in the post-processing module, the first equivalent plastic strain is subtracted by the second equivalent plastic strain at the corresponding node to obtain the equivalent plastic strain increment of each node, and the maximum equivalent plastic strain increment is read according to the equivalent plastic strain increment of each node. It should be noted that the last step of the last cycle of the cold-heat shock cycle is the stress state of the exhaust heat end model calculated by the finite element software at the time when the calculation of the last cycle is completed.

[0086] In an embodiment, the life prediction program is obtained according to the determined prediction model. Specifically, the prediction model is solidified into the life prediction program by using the FORTRAN language. Obtaining the life prediction program according to the determined prediction model further includes: embedding the life prediction program in the ABAQUS software, and realizing the calling and execution of the life prediction program in the form of the ABAQUS software interface operation button. Specifically, a life prediction subprogram embedded in the ABAQUS software is developed, and the calling and execution of the life prediction program is realized in the form of the ABAQUS software interface operation button.

[0087] In an embodiment, the maximum equivalent plastic strain increment of the exhaust heat end is substituted into the life prediction program according to the determined prediction model, and the predicted life of the exhaust heat end is obtained. Specifically, in the development stage, the stress field analysis is performed on the exhaust heat end model according to the actual working condition of the engine, the maximum equivalent plastic strain increment of the exhaust heat end and the temperature value at the node of the maximum equivalent plastic strain increment are obtained, the temperature value at the maximum equivalent plastic strain increment is input into the prediction program to read the fatigue ductility coefficient and the fatigue extension index of the material of the check component, and then the read fatigue ductility coefficient and fatigue extension index and the maximum equivalent plastic strain increment of the exhaust heat end are input into the prediction program to obtain the life prediction calculation result of the exhaust heat end. It should be noted that the prediction program includes a first prediction program and a second prediction program, the first prediction program obtains the fatigue ductility coefficient and the fatigue extension index of the material of the check component according to the input temperature value at the maximum equivalent plastic strain increment, the second prediction program takes the fatigue ductility coefficient and the fatigue extension index obtained by running the first prediction program and the maximum equivalent plastic strain increment of the exhaust heat end calculated by the finite element software as input values, and runs the second prediction program to obtain the predicted life of the exhaust heat end.

[0088] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the present application; although the present application has been described in detail with reference to the foregoing examples, the technical solutions recorded in the foregoing examples can still be modified by those skilled in the art, or some technical features thereof can be replaced by equivalent replacements; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present application.

Claims

1. A method for establishing a prediction model of low cycle fatigue life of exhaust gas hot end, characterized in that, The method comprises: establishing an exhaust heat end model; setting thermal boundary conditions of the exhaust heat end model according to the engine at different powers; performing stress field analysis on the exhaust heat end model based on each thermal boundary condition to obtain a strain increment table of the maximum equivalent plastic strain increment of the exhaust heat end and a temperature table of the node position corresponding to the maximum equivalent plastic strain increment; determining a life checking component according to the maximum equivalent plastic strain increment of the exhaust heat end; performing high-temperature tensile tests on the life checking component based on the temperature table to obtain a static tensile fracture strain table of the material of the life checking component at the corresponding temperature; performing cold and hot impact cycle tests on the life checking component based on the temperature table to obtain a test life table of the life checking component at the corresponding temperature; determining the prediction model according to the static tensile fracture strain table, the test life table, and the strain increment table, wherein the prediction model is used to predict the low-cycle fatigue life of the exhaust heat end; and the step of determining the prediction model according to the static tensile fracture strain table, the test life table, and the strain increment table specifically comprises: determining a fatigue ductility coefficient table of the life checking component according to the static tensile fracture strain table of the life checking component; determining a fatigue ductility index table of the life checking component according to the fatigue ductility coefficient table, the test life table, and the strain increment table; obtaining the prediction model according to the fatigue ductility coefficient table and the fatigue ductility index table, and the expression of the prediction model is: wherein, for predicting the life, C is a fatigue ductility coefficient, is a fatigue ductility index, is a maximum equivalent plastic strain increment.

2. The prediction model establishment method of claim 1, wherein, the thermal boundary conditions of the exhaust heat end model include: forced convective heat transfer between high-temperature gas and the inner surface of the exhaust heat end, free convective heat transfer between engine cabin air and the outer surface of the exhaust heat end, thermal radiation between the exhaust heat end and the heat shield, and thermal conduction of the intake flange and the cylinder head.

3. The method of claim 1, wherein the step of establishing the predictive model comprises the step of: The thermal boundary conditions of the exhaust heat end further include boundary conditions at the turbine outlet, wherein the boundary conditions at the turbine outlet are obtained according to the turbine inlet mass flow, the rotational speed of the turbine blade, and the rotation angle of the turbine blade. ​ 4. The method of claim 1, wherein the step of establishing the predictive model comprises the step of: The step of obtaining the strain increment table of the maximum equivalent plastic strain increment of the exhaust heat end specifically comprises: ​ setting a cold and hot impact analysis step of the exhaust heat end model; performing sequential coupled thermal stress analysis on the exhaust heat end model based on the cold and hot impact analysis step to obtain the maximum equivalent plastic strain increment of the exhaust heat end; tabulating different maximum equivalent plastic strain increments to obtain the strain increment table of the maximum equivalent plastic strain increment.

5. The method of claim 4, wherein the step of establishing the predictive model is performed by a computer system. The cold and hot impact analysis step is greater than or equal to three cold and hot impact cycles.

6. The method of claim 4, wherein the step of establishing the predictive model is performed by a computer system. The step of performing sequential coupled thermal stress analysis on the exhaust heat end model based on the cold and hot impact analysis step to obtain the maximum equivalent plastic strain increment of the exhaust heat end specifically comprises: Each of the maximum equivalent plastic strain increments in the strain increment table is based on sequentially coupled thermal stress analysis to obtain a first equivalent plastic strain at each node of the hot gas path model at the last step of the last cycle of the cold-heat shock cycle; sequentially coupled thermal stress analysis to obtain a second equivalent plastic strain at the each node of the hot gas path model at the last step of the second last cycle of the cold-heat shock cycle; subtracting the second equivalent plastic strain at the each node from the first equivalent plastic strain at the each node to obtain an equivalent plastic strain increment at the each node, and obtaining the maximum equivalent plastic strain increment based on the equivalent plastic strain increment at the each node.

7. The method of claim 1 to 6, wherein Further comprising the following steps: obtaining a life prediction program according to the prediction model.

8. The method of claim 7, wherein the step of establishing the predictive model is performed by a computer system. The prediction model obtaining life prediction program further comprises: embedding the life prediction program in ABAQUS software, and realizing the calling and execution of the life prediction program in the form of interface operation buttons of the ABAQUS software.

9. The method of claim 8, wherein the step of establishing the predictive model is performed by a computer system. According to the prediction model determined, the maximum equivalent plastic strain increment of the hot gas path is substituted into the life prediction program to obtain the predicted life of the hot gas path.

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